A blood clot or thrombus is formed as a result of coagulation. It is composed of aggregated platelets and erythrocytes which act like a plug, and polymerized fibrins which act as a mesh. The forming of blood clots help to put a stop on blood leaking through injured vasculatures big and small. But their presence in veins and arteries can also lead to devastating consequences such as stroke, heart attack, and pulmonary embolism, in which they obstruct blood flow to vital organs. Patients who have atrial fibrillation, heart valve replacement, myocardial infarction, or just extended periods of inactivity would have increased risk of thrombosis.
18F-GP1 PET images show blood clots present in catheterized veins and arteries. Gallbladder accumulation of the tracer is also visible. Credit: Piramal Imaging GmbH#
The current line of diagnostic tools for thrombosis (ultrasound, venography, magnetic resonance imaging and computed tomography) rely heavily on the characteristics of thrombi structure and pay no attention to the biology of the clots. A team of German researchers has developed 18F-GP1, a Fluorine-18 (a positron emitting isotope) labeled ligand that specifically targets GPIIb/IIIa receptors the key player in coagulation. GPIIb/IIIa receptors, or glycoproteins IIb/IIIa, belong to integrin complex found mostly on platelets. They allow for the binding of fibrinogen and von Willebrand factor, which leads to the activation of platelets.
In a recent report published in the Journal of Nuclear Medicine, the group demonstrated that 18F-GP1 has a high affinity to blood clots. The administration of anticoagulants like aspirin and heparin did not affect the binding of the ligand. Using PET (positron emitting tomography) scan, they were able to detect thrombus at various locations and of different size. The encouraging results from animal studies motivated the team to put 18F-GP1 through clinic trial.
The investigators have expressed high hope for the blood clot-detecting tracer. As the leader of the group Dr. Andrew W. Stephens stated: "Although the current studies are preliminary, 18F-GP1 may provide not only more accurate anatomic localization, but also information of the risk of the clot growth or embolization. This may lead to changes in clinical intervention to the individual patient."
#This study was funded by Bayer Pharma AG and Piramal Imaging GmbH, Berlin, Germany.